1. Field of the Invention
This invention relates to a pane antenna for automobiles, in which an antenna conductor is disposed on the surface of or inside an automobile glass pane. The antenna feed point is connected to the central conductor of a coaxial cable and is disposed in the vicinity of a conductive area located in the edge region of the glass pane and connected to the sheath of the coaxial cable.
2. Description of the Related Art
Antenna structures of this type are suitable as signal transmission antennas for radio communication, especially as antennas for digital radio telephone communication. For maximum transmission efficiency, such antennas must be precisely tuned. They require, for this purpose, a defined reference plane to which all electrical parameters are referred. As the reference plane, therefore, a strip-shaped, electrically conducting coating is disposed directly on the edge region of the glass pane.
An antenna structure of this type is known from WO 88/09569. In this known antenna, which is intended for use as a radio antenna, preferably for the frequency range from 890 to 960 MHz, the antenna conductor consists of a rectilinear conductor having a free end which projects from the edge of the glass pane into the viewing field of the glass pane. The antenna conductor having a conductive area and acting as a reference plane can be printed and baked onto the surface of the glass pane facing towards the interior of the vehicle, like heating conductors for heating panes.
The resonance frequency of this known antenna structure exhibits a certain dependence upon the materials of the glass pane and upon the geometrical tolerances necessary for installation of the glass pane. With these known antennas, therefore, it is still necessary to tune them again after installation if they are to possess an optimum efficiency.